The way I see it, this issue cuts based on whether one believes we are really at war. Those who believe we are tend to support some temporary limits on personal privacy, be it monitoring international communications or having to have your backpack checked to ride the NYC subway.
But those who do not believe this is really a war, or feel terrorism is not really a serious threat, or who want Americans to forget 9/11, they've decided to use this issue to basically "rip America out of its war footing," so to speak, or to simply damage President Bush.
For those who believe we are at war, but who also have some concerns about privacy and freedom issues, please note that during most of its wars Americans have experienced some limits on their freedom, but these have always been temporary--the "slipery slope" argument just doesn't hold up.
I pretty much agree with what you wrote. But, sometimes things do get out of hand.
The World War I era provides an example.
In January (1916), under authority of a special act of the 35th legislature, a Loyalty Ranger Force was authorized, to consist of approximately three picked men from each county in Texas. The duties of this force were to act as a secret service department for the State and work in conjunction with all Federal, State, county and municipal officers in the execution of all State laws, especially House Bill No. 15, better known as the "Hobby Loyalty Act." Through the assistance of the loyalty secret service department, the Adjutant General was kept advised as to the Mexican revolutionary activities carried on, principally outside of San Antonio and in the border counties in Mexico and Texas.
As you point out, our secret service was a temporary action. But, during their short careers the Loyalty Rangers inflicted a lot of pain and some injustice.
I don't see the War on Terror being a temporary action. In 1898 we started fighting a Muslim insurgency in the Philippines. As allies with the present Philippine government, we're still fighting their descendents. I don't think the threat from fundamental Muslim terrorists will be any less short lived.
If I'm right, and I hope I'm wrong, the temporary measures you describe may be extended a wee bit further into the future.